The invention relates to an electrical pulp testing instrument comprising a handpiece to accommodate a charge storage device, such as a battery as source of supply and an electrical circuit arrangement to generate a stimulating current variable as to its strength.
In an instrument known from prior art (U.S. Pat. No. 3,943,919) the stimulating current is varied by way of a potentiometer which is to be adjusted manually by means of a knurled disc arranged externally at the handpiece. This kind of adjustment of the intensity requires a relatively high consumption of current, on the one hand, on account of the potentiometer inserted as compensating resistance and on the other hand because of the connecting time left to the physician based on the individual manual operation. The consequence of the increased current consumption is that the charge storage means in the handpiece must be replaced and/or recharged more frequently than desirable. Because of the patient resistance fluctuating very much from patient to patient and the transfer resistance between electrode and tooth, moreover, no satisfactory linearity can be accomplished in the setting of the intensity. The patient and transfer resistances placed parallel with the setting resistance for regulating the intensity in fact are relatively high and thus exert a non-negligible influence on the output current of the pulp testing instrument.